This invention relates to the field of guidewires for advancing intraluminal devices such as stent delivery catheters, balloon dilatation catheters, atherectomy catheters and the like within body lumens.
In a typical coronary procedure a guiding catheter having a preformed distal tip is percutaneously introduced into a patient""s peripheral artery, e.g. femoral or brachial artery, by means of a conventional Seldinger technique and advanced therein until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. There are two basic techniques for advancing a guidewire into the desired location within the patient""s coronary anatomy, the first is a preload technique which is used primarily for over-the-wire (OTW) devices and the bare wire technique which is used primarily for rail type systems. With the preload technique, a guidewire is positioned within an inner lumen of an OTW device such as a dilatation catheter or stent delivery catheter with the distal tip of the guidewire just proximal to the distal tip of the catheter and then both are advanced through the guiding catheter to the distal end thereof. The guidewire is first advanced out of the distal end of the guiding catheter into the patient""s coronary vasculature until the distal end of the guidewire crosses the arterial location where the interventional procedure is to be performed, e.g. a lesion to be dilated or a dilated region where a stent is to be deployed. The catheter, which is slidably mounted onto the guidewire, is advanced out of the guiding catheter into the patient""s coronary anatomy over the previously introduced guidewire until the operative portion of the intravascular device, e.g. the balloon of a dilatation or a stent delivery catheter, is properly positioned across the arterial location. Once the catheter is in position with the operative means located within the desired arterial location, the interventional procedure is performed. The catheter can then be removed from the patient over the guidewire. Usually, the guidewire is left in place for a period of time after the procedure is completed to ensure reaccess to the arterial location is it is necessary. For example, in the event of arterial blockage due to dissected lining collapse, a rapid exchange type perfusion balloon catheter such as described and claimed in U.S. Pat. No. 5,516,336 (McInnes et al), can be advanced over the in-place guidewire so that the balloon can be inflated to open up the arterial passageway and allow blood to perfuse through the distal section of the catheter to a distal location until the dissection is reattached to the arterial wall by natural healing.
With the bare wire technique, the guidewire is first advanced by itself through the guiding catheter until the distal tip of the guidewire extends beyond the arterial location where the procedure is to be performed. Then a rail type catheter, such as described in U.S. Pat. No. 5,061,395 (Yock) and the previously discussed McInnes et al. which are incorporated herein by reference, is mounted onto the proximal portion of the guidewire which extends out of the proximal end of the guiding catheter which is outside of the patient. The catheter is advanced over the catheter, while the position of the guidewire is fixed, until the operative means on the rail type catheter is disposed within the arterial location where the procedure is to be performed. After the procedure the intravascular device may be withdrawn from the patient over the guidewire or the guidewire advanced further within the coronary anatomy for an additional procedure.
Conventional guidewires for angioplasty, stent delivery, atherectomy and other vascular procedures usually comprise an elongated core member with one or more tapered sections near the distal end thereof and a flexible body such as a helical coil or a tubular body of polymeric material disposed about the distal portion of the core member. A shapable member, which may be the distal extremity of the core member or a separate shaping ribbon which is secured to the distal extremity of the core member extends through the flexible body and is secured to the distal end of the flexible body by soldering, brazing or welding which forms a rounded distal tip. Torquing means are provided on the proximal end of the core member to rotate, and thereby steer, the guidewire while it is being advanced through a patient""s vascular system.
Further details of guidewires, and devices associated therewith for various interventional procedures can be found in U.S. Pat. No. 4,748,986 (Morrison et al.); U.S. Pat. No. 4,538,622 (Samson et al.): U.S. Pat. No. 5,135,503 (Abrams); U.S. Pat. No. 5,341,818 (Abrams et al.); U.S. Pat. No. 5,345,945 (Hodgson, et al.) and U.S. Pat. No. 5,636,641 (Fariabi) which are hereby incorporated herein in their entirety by reference thereto.
For certain procedures, such as when delivering stents around challenging take-off, e.g. a shepherd""s crook, tortuosities or severe angulation, substantially more support and/or vessel straightening is frequently needed from the guidewire than normal guidewires can provide. Guidewires have been commercially introduced for such procedures which provide improved distal support over conventional guidewires, but such guidewires are not very steerable and in some instances are so stiff that they can damage vessel linings when advanced therethrough. What has been needed and heretofore unavailable is a guidewire which provides a high level of distal support with acceptable steerability and little risk of damage when advanced through a patient""s vasculature.
In addition, conventional guidewires using tapered distal core sections as discussed above can be difficult to use in many clinical circumstances because they have an abrupt stiffness change along the length of the guidewire, particularly where the tapered portion begins and ends. As a guidewire having a core with an abrupt change in stiffness is moved through tortuous vasculature of a patient, the physician moving the guidewire can feel the abrupt resistance as the stiffness change is deflected by the curvature of the patient""s vasculature. The abrupt change in resistance felt by the physician can hinder the physician""s ability to safely and controllably advance the guidewire through the vasculature. What has been needed is a guidewire, and particularly a guidewire core member, that does not have an abrupt change in stiffness, particularly in the portions of the distal section that are subject to bending in the vasculature and guiding catheter. The present invention satisfies these and other needs.
The present invention is directed to an improved guiding device providing enhanced distal support while having a flexible distal tip to provide acceptable steerability and little risk of damage to vessel or chamber linings when advanced through a patient""s body lumen such as veins and arteries.
The guiding member of the present invention has an elongated core member with proximal and distal core sections and a flexible tubular body such as a helical coil disposed about and secured to the distal section of the core member. The distal core section has a plurality of distally tapering contiguous core segments having tapers of up to 25xc2x0 and lengths of up to 15 cm. As used herein the measurement of tapers is the angle of a line tangent to the surface of the segment in line with the longitudinal axis of the core member. The first tapered core segment, which typically has a circular transverse cross-section, preferably tapers from the diameter of the adjacent proximal core section to a diameter of about half to about three quarters of the diameter of the adjacent proximal core section. The second tapered core segment, which also has a circular transverse cross-section, tapers from the smallest diameter of the first tapered core segment to a diameter of not more than one-half the smallest diameter of the first tapered core segment.
One presently preferred embodiment includes a first core segment with a taper in the distal direction and a distally contiguous second core segment having a taper in the distal direction greater than the taper of the first core segment. The taper of the first or proximal segment generally can be up to about 5xc2x0, preferably about 0.01xc2x0 to about 1xc2x0, more preferably about 0.011xc2x0 to about 0.20xc2x0. The taper of the second or distal core segment can be up to about 6xc2x0, preferably about 0.01xc2x0 to about 1.1xc2x0, more preferably about 0.015xc2x0 to about 0.45xc2x0.
In another presently preferred embodiment, the second tapered core segment has a length greater than the first tapered core segment with the distal segment generally ranging about 1 to about 12 cm, preferably about 2 to about 10 cm and the distal segment generally about 1 to about 8 cm, preferably about 2 to about 6 cm. The tapered core segments may have circular transverse cross-sections and straight exterior surfaces, e.g. frusto-conical shape. However, other shapes are contemplated, e.g. curved exterior surfaces. Indeed, the taper of the contiguous core segments may have a continuously changing taper over all or part of both core segments.
The flexible tubular body such as a helical coil is secured by its distal end to the distal tip of the distal core section or to the distal tip of a shaping ribbon secured to the distal core section in a conventional fashion. The helical coil may be secured by its distal end by soldering, brazing or welding to form a rounded distal tip to the guiding member as done with commercially available guidewire for procedures within a patient""s coronary artery.
In one presently preferred embodiment of the invention, the guidewire has an elongated proximal core section having a length of about 65 to about 280 cm and a circular transverse cross-section with a diameter of generally about 0.010 to about 0.035 inch (0.30-0.46 mm), typically about 0.012 to about 0.018 inch (0.30-0.46 mm) for coronary anatomy.
In one presently preferred embodiment of the invention, the second tapered core segment is preferably followed distally with a manually shapable flattened core segment of about 1 to 4 cm in length which preferably has essentially constant transverse dimensions, e.g. 0.001 by 0.003 inch (mm). A helical coil having transverse dimensions about the same as the proximal core section is secured by its distal end to the flattened distal tip of the core member, e.g. solder, and by its proximal end at an intermediate position on the second tapered segment so that the distal end of the second tapered segment resides within the interior of the coil. The coil may have a length of about 2 to about 40 cm or more, but typically will have a length of about 2 to about 10 cm in length.
The guidewire of the invention provides the enhanced distal and proximal support needed for stent deployment, advancement of atherectomy devices and the like and provides a smooth transition between the proximal core section and the flattened distal tip of the core member while exhibiting excellent steerability.
In another aspect of the invention, an intracorporeal device, preferably a guidewire, has an elongated member with at least one longitudinal section having a substantially linear change in stiffness over a length thereof. A substantially linear change in stiffness of a section of an elongate intracorporeal device may be achieved with an elongate core member having a tapered profile, tapering distally to a smaller transverse dimension and configured to produce a linear change in stiffness. The distal taper of the elongate core may be in the form of a taper having a continuously changing taper angle, i.e. a curvilinear taper profile, or may be achieved by a plurality of tapered segments which are longitudinally short in comparison to the longitudinal length of the tapered section as a whole.
In embodiments where a plurality of tapered segments are used, the tapered segments are preferably contiguous or adjacent each other and have a substantially constant taper angle over the length of each tapered segment. In a preferred embodiment, the taper angle of each tapered segment is greater than the taper angle of the segment proximally adjacent to it. The taper angle and segment length can be controlled from tapered segment to tapered segment to produce the desired bending characteristics of the longitudinal section of the core member.
A core member may be ground to a profile which is calculated mathematically to produce a linear change in stiffness. A useful formula for generating a substantially linear change in stiffness is       D    L    =            [                                    64            ⁢            CL                                E            ⁢                          xe2x80x83                        ⁢            π                          +                  D          0          4                    ]              1      4      
where DL is the diameter of an elongate core member at length L from a position of starting diameter D0, E is the modulus of elasticity of the material from which the elongate core member is made, and C is a constant.
This formula may be used to generate smooth continuous profiles, or multiple tapered segments where each individual tapered segment has a substantially constant taper angle. In the latter instance, the taper angle and length of each tapered segment can vary to produce the overall desired effect by having the segmented contour substantially follow the formula above. In a preferred embodiment, the points between two adjacent tapered segments, or transition points, have diameters that substantially follow the formula above for DL. As the number of tapered segments increases, this embodiment gradually approaches the smooth continuous curvilinear embodiment. That is, in the limiting case where the number of tapered segments is large, there is little or no difference in stiffness between the segmented core and the smooth curvilinear profile core.
Another approach to generating linear stiffness change in an elongate intracorporeal involves controlling the moment of inertia at any given point in a longitudinal section. A useful formula for such an approach is       I    L    =            CL      E        +          I      0      
where IL is the moment of inertia of the elongate core member at length L from a position of starting inertia I0, E is the modulus of elasticity of the core material, and C is a constant that is derived from the boundary conditions of the longitudinal section, specifically, a desired starting moment of inertia, finish moment of inertia, length of section of linear change in stiffness.
A core member with a linear change in stiffness over its length provides improved advancement and control of the distal end of an intracorporeal device through a patient""s body lumen. The improvement in handling characteristics results in part from the absence of abrupt changes in flexibility that can obscure the tactile feedback to the physician holding the proximal end of the device. In addition, the abrupt changes in stiffness can cause the device to resist smooth and controllable advancement because a step or threshold force must be applied to overcome the abrupt change in stiffness.
These and other advantages of the invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying exemplary drawings.